Magnetic recording media, which include magnetic tape and magnetic disks, are used for storage and retrieval of data. The data are encoded in magnetizations on the recording surface. In particular, the data are encoded in transitions, which represent boundaries between regions of magnetization reversal.
There are two parts to a magnetic recording system. The first part is the magnetic recording medium, which holds the data. A typical magnetic recording medium consists of a thin layer of ferromagnetic material, such as gamma ferric oxide, supported by a non-magnetic substrate. The ferromagnetic material is a material that can be permanently magnetized upon application of an external magnetic field. The ferromagnetic material normally includes magnetic particles mixed with a binder to attach it to the non-magnetic substrate.
The second part to a magnetic recording system is the recording head, which applies the external magnetic field that magnetizes the magnetic recording medium. The recording head is an electromagnet that typically comprises ferromagnetic C-shaped core wrapped with a wire coil. The core includes a very narrow gap that is positioned near the magnetic recording medium.
The recording head is energized when current flows through the coil. Current in the coil induces a magnetic flux in the core and causes a fringing magnetic field, also called the recording field, to be generated across the gap. The recording field, which normally has an arcuate or substantially circular profile, extends from the gap through the magnetic recording medium. The recording field gradient is sharper near the gap and broader further from the gap. When the recording field passes through the magnetic recording medium, a remnant magnetization is created on the ferromagnetic surface. This results in a permanent magnetization of the ferromagnetic surface.
When any data stored magnetically are recovered from a magnetic recording medium, there is a risk that the data are contaminated with noise. Generally speaking, noise represents undesirable, unpredictable and random signals. In creating a magnetic recording system, it is desirable to identify sources of noise and, if possible, to reduce or eliminate them.